Cluster-exact approximation applied to adsorption with non-additive lateral interactions

Abstract

The adsorption of single particles with non-additive lateral interactions has been studied by combining Monte Carlo (MC) simulations and theoretical modeling. The traditional assumption of additive lateral interactions is replaced with a more general one including non-pairwise interactions. It is assumed that the energy linking a certain atom with any of its nearest neighbors strongly depends on the state of occupancy in the first coordination sphere of such an adatom. Two theoretical models have been used in the present study: (i) the first, which we called cluster-exact approximation (CA), is based on exact calculations of configurations on finite cells. An efficient algorithm allows us to calculate the detailed structure of the configuration space for m=l×l cells; and (ii) the second is a generalization of the classical quasi-chemical approximation (QCA) in which non-additive lateral interactions have been included. The process is monitored by following the surface coverage as a function of the chemical potential (adsorption isotherm). Results from CA and QCA are compared with MC simulations. A good agreement is obtained between theoretical and MC results, with CA being the most accurate approximation in all cases. This finding supports the validity of the exact counting of states on finite cells as a starting point to predict the behavior of a system governed by non-additive lateral interactions.